This invention relates to wireless communication systems, and more particularly, to wireless communication systems using multiple antennas at the transmitter and one or more antennas at the receiver.
Wireless communication systems that use multiple antennas at the transmitter are commonly referred to as multiple-input systems. Space-time coding can be used in multiple-input systems to reduce the power needed to transmit information at a particular information data rate and still maintain a certain error rate. Similarly, space-time coding can be used to increase the information data rate at a particular power lever and still maintain a certain error rate, or to reduce the error rate at a particular information data rate and power level.
Additionally, it is highly advantageous to employ channel coding in order to approach the maximum open loop capacity of a multiple-input system. (An open loop system is one where channel characteristics are not fed back to the transmitter.) As channel coding improves, the system approaches the maximum open loop capacity. Thus, it is desirable to employ such channel coding in a multiple-input system. The state-of-the-art channel codes, e.g., Turbo codes, trellis codes and the like, are typically spatially one dimensional, i.e., they are designed for only a single transmit antenna. Particular types of space-time coding allow the use of such channel codes in multiple-input systems. Such space-time coding involves reducing interference between concurrently transmitted symbols.
Typically, in a transmitter that uses both channel coding and space time coding, a primitive data stream—the data stream to be transmitted—is divided into data sub-streams, each of which is channel coded, and each encoded sub-stream is mapped into symbol space to produce symbol sub-streams. One or more of the symbol sub-streams are then space-time coded to form space-time coded symbol sub-streams. In some space-time coding schemes, each transmit antenna transmits transmit-sequences formed from the symbols of one or more symbol sub-streams. The transmit-sequences are one or more symbol periods in duration. This duration is commonly referred to as the length of the transmit-sequence. A plurality of transmit-sequences that are to be transmitted by the same antenna form the space-time-coded symbol sub-streams.